HelenOS sources

islower            37 common/stdc/ctype.c int islower(int c)
islower            37 kernel/generic/common/stdc/ctype.c int islower(int c)
islower           105 kernel/generic/include/macros.h #define islower(c)     (((c) >= 'a') && ((c) <= 'z'))
islower            37 uspace/lib/c/common/stdc/ctype.c int islower(int c)
islower            85 uspace/lib/cpp/include/__bits/locale/locale_misc.hpp     bool islower(Char c, const locale& loc)