"Implication" has two uses:

Implication in (1) logical relation:

A implies B: A and B are propositional formulas; -There is obviously no comma in the propositional formula;

(2) Implication in reasoning

A 1, A2, A3 contains b: it means that (A 1 conjunctive A2 conjunctive A3) contains b;

"Conjunction" constructs (A 1, A2, A3) into a propositional formula. Therefore, the latter formula is an application of the formula in (1).

There is only one usage of "equivalence": logical relationship;

A is equivalent to b; Same as (1), A and B must be propositional formulas;

We can say that (A 1 conjunctive A2 conjunctive A3) is equivalent to B, or B is equivalent to (A 1 conjunctive A2 conjunctive A3), but we can't say that A 1, A2 and A3 are equivalent to B; Because (A 1, A2, A3) is not a propositional formula-that's all.

The reasoning in (2) is one-way, and "a proposition" can only be deduced from "a set of propositions", but not the other way around-this is the definition.

Even if (A 1, A2, A3) and (b) are logically equivalent; We can't say:

B implication (A 1, A2, a3);

But we can only say: b implication (A 1 conjunctive A2 conjunctive A3);

Or: b contains A 1, b contains A2, and b contains a3; -This is the third application of (1) or (2). When there is no comma, (1) and (2) have no difference in form.

"Comma" does have the same meaning as "conjunction", but the usage of things with the same meaning is not necessarily the same. This is especially true in mathematics, such as "implication (=>)" and "conditional conjunction (→)".