$\mathrm{dsolve}\left(\left\{\mathrm{diff}\left(f\left(x\right)\,x\right)\=g\left(y\right)\right\}\,\mathrm{numeric}\right)\;$

Error, (in dsolve/numeric/process_input) input system must be an ODE system, got independent variables {x, y}

$\mathrm{dsolve}\left(\left\{\mathrm{diff}\left(f\left(x\right)\,x\right)\=f\left(x\right)\,\mathrm{diff}\left(g\left(y\right)\,y\right)\=-g\left(y\right)\,f\left(0\right)\=1\,g\left(0\right)\=-1\right\}\,\mathrm{numeric}\right)\;$

Error, (in dsolve/numeric/process_input) input system must be an ODE system, got independent variables {x, y}

$\mathrm{dsolve}\left(\left\{\mathrm{diff}\left(f\left(x\right)\,x\right)\=f\left(x\right)\,f\left(0\right)\=1\right\}\,\mathrm{numeric}\right)\,\mathrm{dsolve}\left(\left\{\mathrm{diff}\left(g\left(y\right)\,y\right)\=-g\left(y\right)\,g\left(0\right)\=-1\right\}\,\mathrm{numeric}\right)\;$

$\mathbf{proc}\left(\mathrm{x\_rkf45}\right)...\mathbf{end\; proc}\,\mathbf{proc}\left(\mathrm{x\_rkf45}\right)...\mathbf{end\; proc}$

$\mathrm{dsolve}\left(\left\{\mathrm{diff}\left(f\left(x\right)\,x\right)\=f\left(x\right)\,\mathrm{diff}\left(g\left(x\right)\,x\right)\=-g\left(x\right)\,f\left(0\right)\=1\,g\left(0\right)\=-1\right\}\,\mathrm{numeric}\right)\;$

$\mathbf{proc}\left(\mathrm{x\_rkf45}\right)...\mathbf{end\; proc}$