Is it permissible and valid to pray in a place that has been trodden by the feet of a pig?

The passage of a pig over land does not render it impure unless its hooves are moist with an impurity such as its urine or sweat. An impure animal does not make something it touches impure unless one of the two parties is moist. The original state of the earth is purity, so it is not rendered impure merely by the passage of a pig over it. Therefore, prayer in a place where a pig has passed is valid, unless its impurity due to the pig's urine or sweat is known.