Simplify callable from a to l #232

Job	Run time
macosx (-O0)	44m 18s
macosx (-O0 -stdlib=libc++, -stdlib=libc++)	41m 43s
linux (g++, -O3 -DNDEBUG)	27m 34s
macosx (-O3 -flto -DNDEBUG)	25m 36s
linux (clang++, -O3 -DNDEBUG)	4m 26s
macosx (-O3 -flto -DNDEBUG -stdlib=libc++, -stdlib=libc++)	24m 7s
linux (g++, -O3 -DNDEBUG -mavx2)	16m 34s
linux (clang++, -O3 -DNDEBUG -mavx2)	42m 51s
linux (g++, -O3 -DNDEBUG -march=skylake-avx512)	27m 8s
linux (clang++, -O3 -DNDEBUG -march=skylake-avx512)	36m 58s
	4h 51m 15s

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