paradox ~ mixing a level with its meta-level

There is no mixing-level problem for the equation

*f*(*x*) = *x*,

because it just means that two variables have the same value. In other words, the value of a function of *x *is equal to the value of *x*.

However, for the equation

*f* = *x*,

there is a mixing-level problem, resulting no meanings; because

the equation means that a function (aka a formula of a number) is equal to a variable (aka a number).

A formula of a number is a structure. It cannot be a number.

— Me@2013-07-16 10:45 AM

2014.10.13 Monday (c) All rights reserved by ACHK