concept of universal IMF by invoking mechanisms such as fragmentation of molecular clouds [@Larson1973] or feedback from the ISM [@Klishin2016]. However, there is no definitive theoretical model that can predict a given universal IMF from first principles, which limits our theoretical understanding of the fundamental physics that govern the IMF.

Should the IMF vary?
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We expect the IMF to vary since a galaxy’s metallicity, SFRs, and environment can change dramatically with time [eg., @Schwarzschild1953; @Larson1998; @Larson2005; @Weidner2013a; @Chattopadhyay2015; @Ferreras2015; @Lacey2016]. Lower metallicities, higher SFRs, and high cloud surface densities prominent at high-redshift can favour the formation of high-mass stars [@Chattopadhyay2015] while interactions between gas clumps in dense environments can suppress the formation of low mass stars [@Krumholz2010]. Furthermore, physically motivated models of early-type galaxies (ETGs) suggest scenarios in which star formation occurs in different periods giving rise to variability in the mass of the stars formed [@Vazdekis1996; @Weidner2013a; @Ferreras2015].

Following from theoretical predictions, recent observational studies have started showing increasing evidence for a non-universal IMF [@Hoversten2008; @vanDokkum2010; @Meurer2011; @Gunawardhana2011; @Cappellari2012; @Cappellari2013; @LaBarbera2013; @Ferreras2013; @Conroy2013b; @Navarro2015a; @Navarro2015d; @Navarro2015c; @Navarro2015b]. These studies investigate both early and late-type galaxies in different physical and environmental conditions and use different techniques to probe the 