求助：关于字符串的减法

没有内置。
s1 = "adsjfaaetffa";
s2 = "ajseh";
delete[str_, char_] :=
With[{pos = StringPosition[str, char]},
If[pos != {}, StringDrop[str, First@pos], str]];
StringSubtract[str1_StringQ, str2_StringQ] :=
Fold[delete, str1, Characters@str2];
StringSubtract[s1, s2]

Fold[StringReplace[#1, #2 -> "", 1] &, s1, Characters[s2]]

...很强大的算法+1