Decode r←[x]⊥y

If x is not provided, it defaults to the scalar 2. If x is a scalar, it is reshaped to the shape of y. Operates on vectors of x and y. The vector y is interpreted in the mixed base defined by x, which is read as a list of weights: each value of y is multiplied with the corresponding value from ⊖×⍆↟¯1↓1⍪⊖x and summed.