∙ Alternant r←(F∙G)y
Applies to matrices of y. F should be a reduction function. r is the alternant, i.e. the generalized determinant, of y, using F and G. If y is a 1x1 matrix, it returns its element. Otherwie, the alternant is computed by finding the minors of y, which are the submatrices formed by deleting each column in order and the first row; next the same alternant is applied to each minor; lastly the subalternants' results are inner-producted (using F and G) with the first row of y: r←(0⊇y)F∙G F∙G⍤2 1↓◡y⊇ᓚ⍨ᓚ~ᓚ⍨⍳≢y. Supports the fill extra argument, which sets the result for empty matrices.