Code Test

#include <stdio.h>
int main(){
    printf("Hello,world\n");
    return 0;
}

\[ \begin{array}{l} \nabla \cdot \mathbf{D} =\rho _f \\ \nabla \cdot \mathbf{B} = 0 \\ \nabla \times \mathbf{E} = -\cfrac{\partial \mathbf{B}}{\partial t } \\ \nabla \times \mathbf{H} = \mathbf{J}_f + \cfrac{\partial \mathbf{D}}{\partial t } \end{array} \]

This is vim on termux test!!!