From type/Allomorph

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method lc(Allomorph:D:)

Calls Str.lc on the invocant's Str value.

From type/Cool

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sub lc(Str(Cool))
method lc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it case-folded to lower case.

say "ABC".lc;       # OUTPUT: «abc␤»

From type/Str

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multi sub    lc(Str:D  --> Str:D)
multi method lc(Str:D: --> Str:D)

Returns a lower-case version of the string.

Examples:

lc("A"); # OUTPUT: «"a"» 
"A".lc;  # OUTPUT: «"a"»