x1 (plural of ordered pairs) is an exhaustive set (possibly infinite) of inputs/outputs defining a unary function which yields result x3 when given input x2; x1(x2) = x3
imaginary i, comma - spherical coordinates: first coordinate gives magnitude (complex modulus/radius) of the number, the second number gives the angle from the positive real axis measured counterclockwise toward the 'positive' imaginary axis (default: in the primary branch/Arg) as measured in some units (which that number should contain; the contextless default will suppose radians); the angle is not normalized.
x1 is the similarity relation between all members of set x2 (set of quoted words) such that they all mean esentially one common thing x3 and are considered to be identical in any meaningful way in language x4.