Question: $A,B,C$ are groups and we know $A\times B\simeq A\times C$. Is $B$ isomorphic to $C$? My work: (1) If $A,B,C$ are finite Abel groups, then this proposition is true, because we just need to compare the invariant factors on both sides. (2) If $A,B,C$ are infinite groups, I constructed a counter-example in which $A$ is direct product of countable