Simsek, Emine, Iro Xenidou-Dervou, Ilyas Karadeniz, and Ian Jones. 2019. “The Conception of Substitution of the Equals Sign Plays a Unique Role in Students’ Algebra Performance”. Journal of Numerical Cognition 5 (1), 24-37. https://doi.org/10.5964/jnc.v5i1.147.