diff --git a/frustration.rs b/frustration.rs
index cbedd52..ef02cfa 100644
--- a/frustration.rs
+++ b/frustration.rs
@@ -2,7 +2,7 @@ use std::io;
 use std::convert::TryInto;
 
 //const CORE_SIZE: usize = 65408
-const CORE_SIZE: usize = 256;
+const CORE_SIZE: usize = 512;
 
 #[derive(Debug, Eq, PartialEq)]
 enum State {
@@ -55,7 +55,7 @@ struct TableEntry {
     immediate: bool
 }
 
-const PRIMITIVES: [TableEntry; 24] = [
+const PRIMITIVES: [TableEntry; 27] = [
     TableEntry {f: ret     , name: None, immediate: false},
     TableEntry {f: lit     , name: None, immediate: false},
     TableEntry {f: add     , name: Some(ShortName {bytes: *b"+  ", length: 1}), immediate: false},
@@ -68,17 +68,20 @@ const PRIMITIVES: [TableEntry; 24] = [
     TableEntry {f: dup     , name: Some(ShortName {bytes: *b"dup", length: 3}), immediate: false},
     TableEntry {f: dump    , name: Some(ShortName {bytes: *b"dum", length: 4}), immediate: false},
     TableEntry {f: from_r_d, name: Some(ShortName {bytes: *b"r> ", length: 2}), immediate: false},
+    TableEntry {f: if_skip  ,name: Some(ShortName {bytes: *b"?  ", length: 1}), immediate: false},
     TableEntry {f: immediate,name: Some(ShortName {bytes: *b"imm", length: 9}), immediate: false},
     TableEntry {f: lbracket, name: Some(ShortName {bytes: *b"[  ", length: 1}), immediate: true},
     TableEntry {f: load    , name: Some(ShortName {bytes: *b"@  ", length: 1}), immediate: false},
     TableEntry {f: mul     , name: Some(ShortName {bytes: *b"*  ", length: 1}), immediate: false},
     TableEntry {f: ret_d   , name: Some(ShortName {bytes: *b"ret", length: 3}), immediate: false},
     TableEntry {f: rbracket, name: Some(ShortName {bytes: *b"]  ", length: 1}), immediate: false},
+    TableEntry {f: smudge  , name: Some(ShortName {bytes: *b"smu", length: 6}), immediate: false},
     TableEntry {f: store   , name: Some(ShortName {bytes: *b"!  ", length: 1}), immediate: false},
     TableEntry {f: sub     , name: Some(ShortName {bytes: *b"-  ", length: 1}), immediate: false},
     TableEntry {f: swap    , name: Some(ShortName {bytes: *b"swa", length: 4}), immediate: false},
     TableEntry {f: tick    , name: Some(ShortName {bytes: *b"'  ", length: 1}), immediate: false},
     TableEntry {f: to_r_d  , name: Some(ShortName {bytes: *b">r ", length: 2}), immediate: false},
+    TableEntry {f: unsmudge, name: Some(ShortName {bytes: *b"uns", length: 8}), immediate: false},
     TableEntry {f: word    , name: Some(ShortName {bytes: *b"wor", length: 4}), immediate: false}
 ];
 
@@ -147,7 +150,11 @@ fn init_dictionary(c: &mut Core) {
 }
 
 fn smudge(c: &mut Core) {
-    c.ram[(c.dp as usize) + 2] ^= 0x40;
+    c.ram[(c.dp as usize) + 2] |= 0x40;
+}
+
+fn unsmudge(c: &mut Core) {
+    c.ram[(c.dp as usize) + 2] &= 0xbf;
 }
 
 fn immediate(c: &mut Core) {
@@ -282,43 +289,14 @@ fn ret_d(c: &mut Core) {
     ret(c);
 }
 
-// --- Inner interpreter ---
-
-fn fetch(c: &mut Core) -> u16 {
-    let ip = c.ip as usize;
-    let opcode = u16::from_le_bytes(c.ram[ip..=ip+1].try_into().unwrap());
-    c.ip += 2;
-    return opcode;
+// --- Control flow ---
+fn if_skip(c: &mut Core) {
+    let truthy = pop(c);
+    let retaddr = from_r(c);
+    to_r(c, retaddr + if truthy == 0 { 2 } else { 0 });
 }
 
-fn execute(c: &mut Core, opcode: u16) {
-    let primitive_index = (65535 - opcode) as usize;
-    if primitive_index < PRIMITIVES.len() {
-        (PRIMITIVES[primitive_index].f)(c);
-    } else {
-        // call
-        to_r(c, c.ip);
-        c.ip = opcode;
-    }
-}
-
-fn step(c: &mut Core) {
-    let opcode = fetch(c);
-    execute(c, opcode);
-}
-
-fn inner(c: &mut Core) {
-    loop {
-        step(c);
-        println!("ip={} trs={}", c.ip, c.trs);
-        if c.trs == 0 {
-            break;
-        }
-    }
-}
-
-// --- Math ---
-
+// --- I/O ---
 fn dot(c: &mut Core) {
     print!("{} ", pop(c));
 }
@@ -337,6 +315,8 @@ fn word(c: &mut Core) {
     }
 }
 
+// --- Math and logic ---
+
 // note: this is an inline primitive, not a dict entry
 fn lit(c: &mut Core) {
     let ip = c.ip as usize;
@@ -368,6 +348,42 @@ fn div(c: &mut Core) {
     push(c, v2.saturating_div(v1));
 }
 
+
+// --- Inner interpreter ---
+
+fn fetch(c: &mut Core) -> u16 {
+    let ip = c.ip as usize;
+    let opcode = u16::from_le_bytes(c.ram[ip..=ip+1].try_into().unwrap());
+    c.ip += 2;
+    return opcode;
+}
+
+fn execute(c: &mut Core, opcode: u16) {
+    let primitive_index = (65535 - opcode) as usize;
+    if primitive_index < PRIMITIVES.len() {
+        (PRIMITIVES[primitive_index].f)(c);
+    } else {
+        // call
+        to_r(c, c.ip);
+        c.ip = opcode;
+    }
+}
+
+fn step(c: &mut Core) {
+    let opcode = fetch(c);
+    execute(c, opcode);
+}
+
+fn inner(c: &mut Core) {
+    loop {
+        step(c);
+        //println!("ip={} trs={}", c.ip, c.trs);
+        if c.trs == 0 {
+            break;
+        }
+    }
+}
+
 // --- Outer interpreter ---
 
 fn lbracket(c: &mut Core) {
@@ -446,6 +462,16 @@ fn main() {
     }
 }
 
-// create : ] create ] [ 65535 ,
-// create ; ] 65535 , [ ' [ , 65535 , immediate
-// : dog 33 . ;
+/*
+create dog ] r> drop  dup .  1 - dup  ? dog ret [
+create dog smudge ] dog ret [ smudge
+100 dog
+
+create : ] create smudge ] [ 65535 ,
+create ; ] unsmudge 65535 , [ ' [ , 65535 , immediate
+: dog 33 . ;
+
+: dog  [ unsmudge ]  r> drop  dup .  1 -  dup ?  dog ;
+: dog  dog ;
+100 dog
+*/