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\mathrm{A}(\mathrm{a})=\int_{\mathrm{a}}^{\mathrm{a}} \mathrm{f}(t) \mathrm{dt}=0, \mathrm{~A}(\mathrm{~b})=\int_{\mathrm{a}}^{\mathrm{b}} \mathrm{f}(t) \mathrm{dt}