Suppose that a system has three states up, partial performance and down. We assume that for a random time <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$$T_1$$</EquationSource> <EquationSource Format="MATHML"> <math xmlns:xlink="http://www.w3.org/1999/xlink"> <msub> <mi>T</mi> <mn>1</mn> </msub> </math> </EquationSource> </InlineEquation> the system is in state up, then it moves to state partial performance for time <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$$T_2$$</EquationSource> <EquationSource Format="MATHML"> <math xmlns:xlink="http://www.w3.org/1999/xlink"> <msub> <mi>T</mi> <mn>2</mn> </msub> </math> </EquationSource> </InlineEquation> and then the system fails and goes to state down. We also denote the...</equationsource></equationsource></inlineequation></equationsource></equationsource></inlineequation>