function state2 = getStateAfterIsoentropicProcessConst(state1, state2, gas)
  state1HasTemperature = isfield(state1, "T") ;
  state2HasPressure    = isfield(state2, "p") ;
  V = getVname(state1) ;
  k = gas.k ;
  if state2HasPressure
    if state1HasTemperature
      equation.variableNames = [ "T"  "p"  "const"] ;
      equation.exponents     = [  k  -(k-1)  -1   ] ;
      otherVariableName      = V ;
    else
      equation.variableNames = [ "p"  V  "const"] ;
      equation.exponents     = [  1   k    -1   ] ;
      otherVariableName      = "T" ;
    end
  else
    equation.variableNames = [ "T"  V  "const"] ;
    equation.exponents     = [  1 (k-1)  -1   ] ;
    otherVariableName      = "p" ;
  end
  variableName = getUnknownVariableNameFromConstEquation(state2, equation) ;
  state2 = updateStateFromConstEquation(variableName, state1, state2, equation) ;
  if isfield(state1, otherVariableName)
    state2.(otherVariableName) = getVariableFromStateEquation(otherVariableName, state2, gas) ;
  end
end