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+# project euler 39
+
+S ← ⧻(
+  ⊸(▽⊸(
+      =/+⊃↙₂⊣°√ ⍉
+    ) ⧅<3 +1⇡⌊÷2)
+  ▽⤚(=/+ ⍉)
+)
+
+# same as S but filters in different order
+S′ ← ⧻(
+  ⊸(⧅<3 +1⇡⌊÷2)
+  ▽⤚(=/+ ⍉)
+  ▽⊸(=/+⊃↙₂⊣°√ ⍉)
+)
+
+⊢▽⊸(=⟜/↥wait≡poolS′) +1⇡1000
+
+# ⊃($new ⊙◌⍜nowS′|$old ⊙◌⍜nowS) 840
+
+# it seems S' is faster on bigger numbers (roughly), 
+# and it pays off here, barely.