title: Algebraic properties of If-Then-Else and commutative three-valued tests

authors: Soo, Khi-Ui

abstract: This paper establishes a finite axiomatization of possibly non-halting computer programs and tests, with the if-then-else operation. The model is a two-sorted algebra, with one sort being the programs and the other being the tests. The main operation on programs is composition, and 1 and 0 represent the programs skip and loop (i.e. never halts) respectively. Programs are modeled as partial functions on some state space X, with tests modeled as partial predicates on X. The operations on the tests are the usual logical connectives T and F. In addition, there is the hybrid operation of if-then-else, and the test-valued operation H on programs which is true when a program halts, and undefined otherwise. The halting operation H implies that operations of domain D and domain join may also be expressed. When tests are assumed to be possibly non-halting, the evaluation strategy of the logical connectives affects the result. Here we model parallel evaluation, as opposed to the common sequential (or short-circuit) evaluation strategy. For example, we view α β as false if either α or β is false, even if the other does not halt.

text: Algebraic properties of If-Then-Else and commutative three-valued tests This paper establishes a finite axiomatization of possibly non-halting computer programs and tests, with the if-then-else operation. The model is a two-sorted algebra, with one sort being the programs and the other being the tests. The main operation on programs is composition, and 1 and 0 represent the programs skip and loop (i.e. never halts) respectively. Programs are modeled as partial functions on some state space X, with tests modeled as partial predicates on X. The operations on the tests are the usual logical connectives T and F. In addition, there is the hybrid operation of if-then-else, and the test-valued operation H on programs which is true when a program halts, and undefined otherwise. The halting operation H implies that operations of domain D and domain join may also be expressed. When tests are assumed to be possibly non-halting, the evaluation strategy of the logical connectives affects the result. Here we model parallel evaluation, as opposed to the common sequential (or short-circuit) evaluation strategy. For example, we view α β as false if either α or β is false, even if the other does not halt.

year: 2019

title: Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough

authors: Duggan, Ian C.

subjects: Constructed waters

abstract: The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.

text: Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.

year: 2012

title: Representations of diversity in the revised New Zealand PictureBook Collection

authors: Daly, Nicola

subjects: picturebooks

abstract: Collections of children’s literature are used for a range of reasons including preservation, record keeping, and more recently the encouragement of intercultural understanding. Both the signifi- cance of learning about other cultures and the importance of children seeing themselves reflected in the books that they read have been discussed extensively. In 2010, the New Zealand PictureBook Collection (NZPBC) was developed in order to create a resource that reflected New Zealand national identity. In 2015 the NZPBC was revised and this article presents a visual and textual analysis of the diversity present in the sixty books nomi- nated through the lens of critical multicultural analysis, using four variables. Findings indicate considerable diversity is present in the collection in terms of representations of ethnicity and family; less so for representations of disability and languages.

text: Representations of diversity in the revised New Zealand PictureBook Collection Collections of children’s literature are used for a range of reasons including preservation, record keeping, and more recently the encouragement of intercultural understanding. Both the signifi- cance of learning about other cultures and the importance of children seeing themselves reflected in the books that they read have been discussed extensively. In 2010, the New Zealand PictureBook Collection (NZPBC) was developed in order to create a resource that reflected New Zealand national identity. In 2015 the NZPBC was revised and this article presents a visual and textual analysis of the diversity present in the sixty books nomi- nated through the lens of critical multicultural analysis, using four variables. Findings indicate considerable diversity is present in the collection in terms of representations of ethnicity and family; less so for representations of disability and languages.

year: 2017