I am a beginner in Stochastic Calculus. I am having trouble understanding the meaning behind a specific notation which appears in the topic of Ito process which in differential notation can be written as
$dX(t)=\mu (t)dt+\sigma (t)dW(t)$
Now it is mentioned as a fact that if $X(0)$, $\mu (t)$ and $\sigma (t)$ are deterministic functions then $X(t)$ is a Gaussian Process with mean and covariance functions given by
$m(t)=X(0)+\int_{0}^{t}\mu (s)ds$, $c(t_{1},t_{2})=\int_{0}^{t_{1}\land t_{2}}\sigma (s)^{2}ds$
I have trouble understanding the upper limit of the integrand appearing the covariance function i.e. $t_{1}\land t_{2}$. What does that mean logically?