Problem Statement

A sub-unit square is a square number (product of two identical non-negative integers) that remains a square after having a 1 subtracted from each digit in the square.

The number 1 is a sub-unit square. 1 - 1 is 0, which is also a square, though it's kind-of a degenerate case. The number 3136 is a sub-unit square. 3136 (56²) with unit 1 subtracted from each digit is 2025 (45²).

A sub-unit square cannot contain a digit zero (0) since zero minus one is negative one. Every known sub-unit square, with the exception of 1, ends with the digits 36.

Let's start with the solution:

allSquares:  map 1..1000000 'x -> x^2
subUnits: allSquares | select 'z -> not? some? digits z 'w -> w=0 
                     | select 'x -> contains? allSquares to :integer join map digits x 'k -> k-1

print ["The first" size subUnits "sub-unit squares:"]
print subUnits