local low = function(i) return string.char(string.byte("a")+i) end
local upp = function(i) return string.char(string.byte("A")+i) end

for i=0,25 do vim.keymap.set("n", "m"..low(i), "m"..upp(i)) end
for i=0,25 do vim.keymap.set("n", "m"..upp(i), "m"..low(i)) end
for i=0,25 do vim.keymap.set("n", "'"..low(i), "'"..upp(i)) end
for i=0,25 do vim.keymap.set("n", "'"..upp(i), "'"..low(i)) end