# Match correct multiplication statements in the domain ^x*\*x*=x*$ using only the ECMAScript subset of regex functionality
# A = first factor; B = second factor; P = number we're testing as the potential product of A and B

^
(?=
    (x?(x*)).         # \1 = A; \2 = A-1, or 0 if A==0;
    (x?(x*))          # \3 = B; \4 = B-1, or 0 if B==0
)
.*=
(?=
    .*
    (                 # \5 = A * B
        (?=\1*$)
        (?=\3*$)
        (?=\1\4+$)
           \3\2+$
    |
        $\1
    |
        $\3
    )
)
\5$