Authors:

In the realm of ideas, of mental objects, those ideas whose properties are reproducible are called mathematical objects, and the study of mental objects with reproducible properties is called mathematics.

Philip J. Davis, Reuben Hersh, Elena Anne Marchisotto (1995). “The Mathematical Experience: Study Edition”, p.441, Springer Science & Business Media
In the realm of ideas, of mental objects, those ideas whose properties are reproducible are called mathematical objects, and the study of mental objects with reproducible properties is called mathematics.