I look for an argument to this statement:
$$ \int_a^x dx_1 \int_a^{x_1} K(x_1,t) dt= \int_a^xdt \int_t^x K(x_1,t) dx_1 $$ It is certainly an integration by change of variables that I can not clarify
I look for an argument to this statement:
$$ \int_a^x dx_1 \int_a^{x_1} K(x_1,t) dt= \int_a^xdt \int_t^x K(x_1,t) dx_1 $$ It is certainly an integration by change of variables that I can not clarify