“…• draw a diagram (Csíkos, Szitányi, & Kelemen, 2012;Novotná, Eisenmann, Přibyl, Ondrušová, & Břehovský, 2014;Pantziara, Gagatsis, & Elia, 2009;Uesaka & Manalo, 2006) • guess and check/trial and error (Capraro, An, Ma, Rangel-Chavez, & Harbaugh, 2012;Elia et al, 2009;Novotná et al, 2015;Novotná et al, 2014;Stacey, 1991) • think of a simpler problem (Goldin & Germain, 1983;Weber & Lockwood, 2014) • analogy (Novotná et al, 2014) • modelling the general on the particular (Goldin, 2010) • look for a pattern (Tanişlf & Õzdaş, 2009) • work backwards Novotná et al, 2014) • make a systematic list Novotná et al, 2014) • auxiliary elements • setting up equations (Novotná et al, 2014) • omitting a condition • subgoals (see section 2.3.5)…”