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b←1=?1e6⍴20 ⋄ b[1]←1

cmpx '(≢¨⊂)⍨b' '-2-/(b/⍳⍴b),1+⍴b'

x←?1e6⍴5e7

cmpx 'b(+/¨⊂)x' '-2-/0,(1⌽b)/+\x'


⍝ (≢¨⊂) and (+/¨⊂) 8 times faster in 15.0