  The graph exploration problem requires a group of mobile robots, initially
placed arbitrarily on the nodes of a graph, to work collaboratively to explore
the graph such that each node is eventually visited by at least one robot. One
important requirement of exploration is the {\em termination} condition, i.e.,
the robots must know that exploration is completed. The problem of live
exploration of a dynamic ring using mobile robots was recently introduced in
[Di Luna et al., ICDCS 2016]. In it, they proposed multiple algorithms to solve
exploration in fully synchronous and semi-synchronous settings with various
guarantees when $2$ robots were involved. They also provided guarantees that
with certain assumptions, exploration of the ring using two robots was
impossible. An important question left open was how the presence of $3$ robots
would affect the results. In this paper, we try to settle this question in a
fully synchronous setting and also show how to extend our results to a
semi-synchronous setting.
  In particular, we present algorithms for exploration with explicit
termination using $3$ robots in conjunction with either (i) unique IDs of the
robots and edge crossing detection capability (i.e., two robots moving in
opposite directions through an edge in the same round can detect each other),
or (ii) access to randomness. The time complexity of our deterministic
algorithm is asymptotically optimal. We also provide complementary
impossibility results showing that there does not exist any explicit
termination algorithm for $2$ robots. The theoretical analysis and
comprehensive simulations of our algorithm show the effectiveness and
efficiency of the algorithm in dynamic rings. We also present an algorithm to
achieve exploration with partial termination using $3$ robots in the
semi-synchronous setting.
