FourSquaresPuzzle←{
⍝ https://perlweeklychallenge.org/blog/perl-weekly-challenge-109/#TASK1
⍝ ⍺: Groups of indices of numbers in ⍵ which share squares
⍝ ⍵: Numbers to be distributed
     ⍵≢⍥≢∪∊⍺:'Invalid input. There must be enough numbers to distribute'
⍝ Example:
⍝ (1 2)(2 3 4)(4 5 6)(6 7) FourSquaresPuzzle ⍳7
     permutations←p⌷⍨⊂⍸1=≢¨(⊂∪)⍤1+/p←⍺⌷⍤0 99⍤1⊢⍵[pmat≢⍵]
     selection←(⍴⍴(0∘≠×≠)∘,)↑⍺   ⍝ Mask to select from each matrix in permutations
     ∊⍤¯1⊢selection⊂⍤(⊢⍤⌿)⍤1⍤99 ¯1⊢permutations
 }