Although an infant's color vision is not as sensitive as an adult's, it is generally believed that babies have good color vision by five months of age. Most babies start crawling at about 8 months old, which helps further develop eye-hand-foot-body coordination.
A language tree, or family tree with languages substituted for real family members, has the form of a node-link diagram of a logical tree structure. Such a diagram contains branch points, or nodes, from which the daughter languages descend by different links.
The grammar G implicitly defines a set of trees: any tree that can be derived from Z using the rule set P is said to be described by G. This set of trees is known as the language of G. More formally, the relation â G on the set T Ï (N) is defined as follows: