Fix typo.

paper/paper.md

@@ -30,7 +30,7 @@ The Python package ``lvlspy`` stores generic quantum level system data, particul
 
 # Statement of Need
 
-Proper modeling of many physical and astrophysical phenomena requires detailed knowledge of the population of constituent atoms, molecules, or nuclei among their discrete energy levels and transition rates between those levels.  For example, calculation of opacity in a stellar atmosphere requires knowledge of the abundance of different species in the atmosphere, the levels in each species, the fraction of each species that exists in a given energy level, and the transition rate to a different level (either spontaneous or induced).  As another example, *astromers*, isotopes with long-lived isomeric states, can provide key information on various astronomical phenomena [@misch2020astromers].  In order to evaluate the importance of a given astromer, howeever, one requires calculation of the effective transition rates between the long-lived isomer and the ground state of the nucleus in a heat bath, which, in turn, requires knowledge of transition rates between energy levels and efficient storage of those rates in an easily managed data structure, such as a matrix [@gupta2001internal].
+Proper modeling of many physical and astrophysical phenomena requires detailed knowledge of the population of constituent atoms, molecules, or nuclei among their discrete energy levels and transition rates between those levels.  For example, calculation of opacity in a stellar atmosphere requires knowledge of the abundance of different species in the atmosphere, the levels in each species, the fraction of each species that exists in a given energy level, and the transition rate to a different level (either spontaneous or induced).  As another example, *astromers*, isotopes with long-lived isomeric states, can provide key information on various astronomical phenomena [@misch2020astromers].  In order to evaluate the importance of a given astromer, however, one requires calculation of the effective transition rates between the long-lived isomer and the ground state of the nucleus in a heat bath, which, in turn, requires knowledge of transition rates between energy levels and efficient storage of those rates in an easily managed data structure, such as a matrix [@gupta2001internal].
 
 Apart from their key role in scientific research, models of quantum level systems provide excellent insight into quantum mechanics.  Energy-level diagrams in a textbook introduce the essential ideas behind such systems, but a simple-to-use software package that allows students to build their own level systems will greatly reinforce those ideas.