diff --git a/fractran.bqn b/fractran.bqn
index 34033e7..334669d 100644
--- a/fractran.bqn
+++ b/fractran.bqn
@@ -31,5 +31,5 @@ RunFractran ← {
 
 seq ← 200 RunFractran 2‿"17/91 78/85 19/51 23/38 29/33 77/29 95/23 77/19 1/17 11/13 13/11 15/14 15/2 55/1"
 •Out "Generated numbers: "∾•Repr seq
-•Out "Primes: "∾•Repr (⌈=⌊)∘(2⊸(⋆⁼))⊸/ seq
+•Out "Primes: "∾•Repr 1↓⌊2⋆⁼(⌈=⌊)∘(2⊸(⋆⁼))⊸/ seq
 
diff --git a/subleq.bqn b/subleq.bqn
new file mode 100644
index 0000000..4d1e85b
--- /dev/null
+++ b/subleq.bqn
@@ -0,0 +1,18 @@
+# Subleq interpreter
+
+_while_ ← {𝔽⍟𝔾∘𝔽_𝕣_𝔾∘𝔽⍟𝔾𝕩}
+ToNum ← {neg ← '-'=⊑𝕩 ⋄ (¯1⋆neg)×10⊸×⊸+˜´·⌽-⟜'0'neg↓𝕩}
+
+Subleq ← {
+  𝕊 memory:
+  {
+    𝕊 ip‿mem:
+    {
+      ¯1‿b‿·: ⟨ip+3, (@-˜•term.CharB@)⌾(b⊸⊑) mem⟩;
+      a‿¯1‿·: •Out @+a⊑mem, ⟨ip+3, mem⟩;
+      a‿b‿c : d ← b-○(⊑⟜mem)a, ⟨(0<d)⊑⟨c, ip+3⟩, d⌾(b⊸⊑) mem⟩
+    } mem⊏˜ip+↕3
+  }  _while_ {𝕊 ip‿mem: ip≥0} 0‿memory
+}
+
+Subleq ToNum¨•args