Easy win in four moves

The following diagram is a problem by Lord Dunsany (Edward John Moreton Drax Plunkett, 18th Baron Dunsany, 1878-1957), who was English man of literature and theatrical writer and good chess player with draws in games against Jose Raoul Capablanca.

A specimen of the poetic expression of Lord Dunsany :
"One art they say is of no use;
The mellow evenings spent at chess,
The thrill, the triumph, and the truce
To every care, are valueless.
"And yet, if all whose hopes were set
On harming man played chess instead,
We should have cities standing yet
Which now are dust upon the dead."

	(Problem 349) Lord Dunsany, "Week-end Problems Book" by Hubert Phillips, 1932 Mate in 4 moves. Two solutions. #4 retro ( 8 + 16 )
[RSBKQBSR/8/8/8/8/8/pppppppp/rsbqkbsr]

The diagram is accompanied by a story : Someone enters in a chess club and sees the pieces arranged this way on a chess board. They inform him "two eccentric gents were playing a game and when the White, who were ready to make a move, announced [Mate in 4 moves, with two ways!] the Black left angry and after him the White left also. Can you discover the continuation?"

While the hero of the story is thinking, can you dear readers find the two solutions of the problem?
If I do not receive comments with the solution, I will publish it soon at the end of this post.