Is a finite semigroup having left cancellation property necessarily a group?

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Is only left cancellation sufficient for a finite semigroup to be a group. Please give proof or counterexample.

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Let $S$ be any nonempty set, and define $xy=y$ for all $x,y\in S.$ Clearly the associative law holds: $(xy)z=z$ and $x(yz)=yz=z.$ The left cancellation property is even easier: $ax=ay\implies x=ax=ay=y.$ However, if $S$ has more than one element, it is not a group. So, to get a counterexample for your question, take $S=\{a,b\}$ with $aa=ba=a$ and $ab=bb=b.$