A researcher inputs a text-based instruction, 'Summarize the following article:', into a language model. The model internally transforms this instruction into a sequence of numerical vectors for processing. Based on common notational standards in this field, how are the original text instruction and its corresponding vector sequence typically denoted?

In the standard notation for language model inputs, a discrete, human-readable prompt is represented by the variable $c$. The sequence of numerical vectors that the model processes, corresponding to this prompt, is denoted as ____.

Match each description of a language model input component with its standard mathematical notation.