| Name | Meaning | MathML | 
| true | Boolean value true | <true/> | 
| false | Boolean value false | <false/> | 
| pi | Mathematical constant pi | <pi/> | 
| avogadro | Value of Avogadro's constant stipulated by SBML | <csymbol encoding="text" definitionURL="http://www.sbml.org/sbml/symbols/avogadro"> avogadro </csymbol/> | 
| time | Simulation time as defined in SBML | <csymbol encoding="text" definitionURL="http://www.sbml.org/sbml/symbols/time"> time </csymbol/> | 
| inf,infinity | Mathematical constant "infinity" | <infinity/> | 
| nan,notanumber | Mathematical concept "not a number" | <notanumber/> | 
Mathematical symbols defined
in the "Level 3" text-string formula syntax.