statistics - What does the superscript used in tennis scores mean

In the score below, what do the 7 and 4 superscripts mean in the first set?

Tennis Scoring Simplified Point System + How To Keep Score

Digital transcriptome profiling of normal and glioblastoma-derived neural stem cells identifies genes associated with patient survival, Genome Medicine

A late-stage assembly checkpoint of the human mitochondrial ribosome large subunit

Tennis set betting odds and statistics

Probability and Tennis

Remote Sensing, Free Full-Text

Tennis Statistics

Probability and Tennis

Tennis explained: Learn the game