utf8.charpattern[\0-\x7F\xC2-\xF4][\x80-\xBF]*§6.4.1

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lua_pushnil[-0, +1, –] void lua_pushnil (lua_State *L); Pushes a nil value onto the stack.

lua_isboolean[-0, +0, –] int lua_isboolean (lua_State *L, int index); Returns 1 if the value at the given index is a boolean, and 0 otherwise.

math.sqrt (x) Returns the square root of x. (You can also use the expression x^0.5 to compute this value.)

lua_tointeger[-0, +0, –] lua_Integer lua_tointeger (lua_State *L, int index); Equivalent to lua_tointegerx with isnum equal to NULL.

luaL_checkstack[-0, +0, v] void luaL_checkstack (lua_State *L, int sz, const char *msg); Grows the stack size to top + sz elements, raising an error if the stack cannot grow to that size. msg is an additional text to go into the error message (or NULL for no additional text).

os.remove (filename) Deletes the file (or empty directory, on POSIX systems) with the given name. If this function fails, it returns nil, plus a string describing the error and the error code. Otherwise, it returns true.

string.find (s, pattern [, init [, plain]]) Looks for the first match of pattern (see §6.4.1) in the string s. If it finds a match, then find returns the indices of s where this occurrence starts and ends; otherwise, it returns nil. A third, optional numeric argument init specifies where to start the search; its default value is 1 and can be negative. A value of true as a fourth, optional argument plain turns off the pattern matching facilities, so the function does a plain "find substring" o

math.deg (x) Converts the angle x from radians to degrees.