Invariant check in token swap program

[anoushk1234]

Why are we comparing invariant here with pool_a.amount * pool_a.amount

program-examples/tokens/token-swap/anchor/programs/token-swap/src/instructions/swap_exact_tokens_for_tokens.rs

Lines 137 to 140 in 4366669

	if invariant > ctx.accounts.pool_account_a.amount * ctx.accounts.pool_account_a.amount {
	return err!(TutorialError::InvariantViolated);
	}