“…The proof of this fact, famous as Strauss' conjecture [31], took almost 20 years and the e¤ort of many mathematicians, beginning with John [13], Glassey [3], Sideris [30], Strauss [32], Zhou [42], and ending with Lindblad and Sogge [19], Georgiev, Lindblad and Sogge [2] and Tataru [33]. The number p w ðNÞ is refered as Strauss critical exponent.…”